The present invention relates to electric shavers and, in particular, it concerns cutter assemblies for such shavers.
Many types of cutter assembly are known for use in electric shavers. In general, the cutting action is provided by a moving blade that passes across the rear surface of a static blade to generate a shearing cutting action. The static blade is generally either in the form of a perforated foil or a radially-slotted circular casing (commonly identified as a "Philips.RTM.-type shaver").
A particular shortcoming associated with electric shavers is their inability to function properly when the growth of hair to be cut exceeds a certain length. A growth of as little as a few millimeters is frequently problematic. The source of this problem is the action of the static blade that generally flattens the hairs against the skin, requiring them to re-erect themselves into cutting engagement within perforations of the static blade. The problem is most acute in shavers employing perforated foils. Even in the case of a radially-slotted static blade, most of the slots not aligned with the direction of movement at any given time, thereby also requiring most of the hairs to flatten and re-erect.
Of some interest in this context is U.S. Pat. No. 2,339,677 to Burns which discloses an early design for a proposed electric shaver in which both the static blade and the moving blade appear to be formed with rows of parallel open-ended slots. Theoretically, such a structure would allow a large proportion of even the longer hairs to enter the slots without being flattened against the skin. In practice, however, the illustrated structure cannot be effectively implemented due to the lack of support for the long isolated strips forming the static blade.
Reference is also made to U.S. Pat. No. 5,390,416 to Uchiyama et al., which discloses a Philips.RTM.-type shaver in which the static blade arrangement is subdivided by a circular groove into separate concentric tracks. Since the material in the region of the groove dips below the depth of the radial slots, the groove region provides a ring of reinforcement for the static blade arrangement. The groove has disadvantages, however, in that there is no continuity between the radials lots of the inner and outer concentric tracks, allowing hairs to slip out through the groove. Additionally, as mentioned above, the radially-slotted static blade requires most of the hairs to flatten and re-erect.
A second shortcoming associated with electric shavers is the heating of the static blade due to friction between the blades during continuous use. All conventional cutter assemblies seem to rely on contact between the fixed and moving blades to provide cutting engagement between the blades. This frictional contact leads to heating of the surfaces that contact the user's skin, causing discomfort and inconvenience.
There is therefore a need for a mechanically feasible cutter assembly structure that would cut even relatively long hairs effectively. It would also be highly advantageous to provide a cutter assembly which would significantly reduce or completely eliminate frictional contact between the moving and static blades, thereby reducing frictional heating, increasing the lifetime of the blades and reducing the power consumption of the shaver.